A New Sensor Element with High Suppression of External Fields for Rotational Speed Sensors in Engine Management Applications 2002-01-2244

Detecting the position of the crankshaft is one of the most essential tasks in modern combustion engines. The general demand for less fuel consumption and less exhaust emissions also yields in harsher requirements for crankshaft sensors regarding phase accuracy. Additionally, future sensors will have to operate under extreme environmental conditions as they will exist in modern engines with new components such as the integrated starter generator.

One of the most promising approaches for rotational speed detection is the use of magnetoresistive sensors in front of a turning gear wheel. These sensors offer a high sensitivity to magnetic fields. Furthermore, the high signal-to-noise-ratio results in a very small phase error due to jitter. This makes the use of MR-technology very attractive for revolution counting with the parallel implementation of additional features, such as misfire detection, for example.

Currently used MR-Sensors are sensitive both to local magnetic field changes caused by a turning gear wheel and to external magnetic fields. In the proximity of new engine components like the integrated starter generator, these sensors require magnetic shielding in order not to be disturbed by large magnetic fields. For this reason, a new generation of engine speed sensors is under development, which combines the described advantages of magnetoresistive technology with a high robustness against disturbances caused by external magnetic fields due to neighbouring engine components.

The new speed sensors will contain both the sensor element and an integrated circuit for signal conditioning. This paper deals with the sensor element, which is the most critical part of the system and mainly determines the overall characteristics of the sensor.